1. Field of the Invention
The present invention is directed to door locking devices and, more particularly, to electromagnetically controlled door locks that are actuatable from remote locations throughout a building. Such locks, known generally as “electric strikes”; are commonly used to prevent the opening of an associated access obstructing member, such as a door, in hotels, offices, apartment buildings, storage cabinets and appliances. In a preferred embodiment the electric strike of the present invention employs a guard clip for deterring picking of the locking mechanism, a springless solenoid designed to prevent the build-up of residual magnetism which otherwise impairs a solenoid's ability upon activation to release the locking mechanism, and a one piece face plate for mounting in a doorjamb which serves to house the electric strike and guide the latch bolt associated with an access obstructing member into engagement with the latch bolt keeper of the electric strike. The present invention is also directed to a method of mounting the one piece face plate and its associated electric strike onto an aluminum doorframe in a manner which requires significantly less cutting of the doorframe by the installation technician than by other methods known in the art.
2. Description of the Related Art
Electronically-operable door strikes installed in a doorjamb to secure a door against opening are known in the art. Electric strikes typically provide a latch bolt keeper mounted on a pivot. The ability of the keeper to rotate on the pivot is electronically controlled. When the keeper is free to rotate to a latch bolt releasing position, the latch bolt associated with the access obstructing member is not retained in the door jamb and the access obstructing member can be opened. When the keeper is not free to rotate, that is, it is in its latch bolt securing position, the latch bolt is retained by the latch bolt keeper, thus securing the door.
Fundamentally, the function of an electric door strike is based on the fact that a retractable stop lever engages the latch bolt keeper and holds it in its latch bolt securing position. That is, the stop lever prevents the latch bolt keeper from rotating. The stop lever is sometimes held in its engaging position with the latch bolt keeper by a lock lever spring-urged into interlocking relationship with the stop lever. To permit the latch bolt keeper to rotate to its latch bolt releasing position, a solenoid is often employed. The solenoid is electronically energized, normally by means of a circuit completing switch remote from the door strike, and the lock lever is moved out of its locking engagement with the stop lever by the action of the solenoid plunger either pulling or pushing the lock lever. The stop lever, no longer being engaged by and being held in position by the lock lever, is incapable of resisting pivoting of the latch bolt keeper when force is applied to the keeper. The keeper is therefore able to be rotated and the door thus able to be opened.
One drawback of some of the electric strikes heretofore available is the ease with which they can be picked open and defeated by the insertion of a tool for unauthorized movement of the latch bolt keeper to a latch bolt releasing position. U.S. Pat. No. 3,638,984 to Davidson and U.S. Pat. No. 3,861,727 to Froerup et al. disclose a latch bolt keeper provided with a lateral edge projection arranged to occupy an overlapping position with respect to an edge of the strike plate and thus close the space between this edge and the adjacent face of the latch bolt keeper so as to provide against the insertion of a picking tool. U.S. Pat. No. 4,026,589 to Hanchett, Jr. also discloses a latch guard which precludes insertion of a tool. Finally, U.S. Pat. No. 4,056,277 to Gamus et al. discloses a plurality of pin-like protrusions positioned to form a barrier to prevent access by a tool to the ball and socket arrangement which serves to hold the latch keeper of that invention in place. Unlike the prior art electric strikes heretofore disclosed, the present invention utilizes a unique guard clip designed to prevent a tool from gaining access to the lock lever and further, by means of its fish hook-like configuration, to redirect any tool which is inserted into the electric strike away from the lock lever and the stop lever.
Another disadvantage of the electric strikes heretofore available is the undesirable build-up of residual magnetism within the solenoid or on the solenoid plunger. It is essential for proper operation of a solenoid that it lose its magnetic force once input electrical power to the solenoid is removed, thus allowing the solenoid plunger to return to its original position. Any magnetic field which remains when electrical power is removed is termed residual magnetism. The residual magnetism present in prior art electric strikes is occasioned by the frequent contact between two ferrous metal surfaces such as a ferrous metal solenoid plunger striking a ferrous metal lock lever during repeated energization and de-energization of the solenoid. Build-up of residual magnetism during repeated cycling of the solenoid results in the eventual failure of the solenoid's ability to remotely disengage the lock lever and the stop lever so as to permit the latch bolt keeper to be rotated and the access obstructing member opened. In some electric strikes termed “fail-safe” or “power to lock” by those of skill in the art, the plunger is pulled into the solenoid body when energized. This action of the plunger pulls the spring-resistive lock lever into engagement with the stop lever, thus preventing the latch bolt keeper from pivoting from its latch bolt securing position to its lockset latch bolt releasing position. When the solenoid is de-energized, the spring-urged lock lever returns to its original position where it is disengaged from the stop lever, thus allowing the latch bolt keeper to be pivoted to its lockset latch bolt releasing position. Upon the build-up of residual magnetism along the plunger or solenoid body, however, the plunger can remain in contact with the lock lever or not fully exit the body of the solenoid, thus compromising the ability of the lock lever to disengage from the stop lever. In the operation of other electric strikes, termed “fail-secure” by those of skill in the art, the plunger is pulled from its starting position into the body of the solenoid upon energization and this action releases the stop lever, thus permitting the latch bolt keeper to rotate. Upon de-energization the plunger exits the solenoid body by means of a spring and is returned to its starting position. Again, however, upon the build-up of residual magnetism along the plunger, the plunger may not be able to be completely returned to its starting position by the spring mechanism, thus compromising the solenoid's ability to return the stop lever or lock lever to a position where the latch bolt keeper is prevented from rotating.
Yet an additional drawback of prior art electric strikes is the large amount of cutting into a steel door jamb which is necessary to install the strike and its associated face plate. The American National Standards Institute (“ANSI”) standard face plate measures 4⅞ inches in length by 1¼ inches in width. Typically, electric strike face plates also utilize an auxiliary ramp which measures 3⅜ inches in length, thus necessitating that a corresponding length of the door jamb be removed at a depth of about one-half inch or more to properly seat the face plate and auxiliary ramp into the jamb. This large amount of cutting requires more time and money to install than otherwise would be necessary with an electric strike and face plate arrangement that reduces the amount of door jamb cutting required for installation.
This problem exists not only in the steel door industry but also in the aluminum/glass door industry which does not follow the ANSI standards. The aluminum/glass door industry manufactures what is commonly known in the trade as “storefronts”. A storefront is a door consisting of a glass panel surrounded and supported by an aluminum frame which is hung from a hollow aluminum doorjamb by means of hinges. A storefront-type entryway is common in many retail establishments such as those found in a strip mall. Architects, designers, and owners of these retail establishments commonly determine the specifications for the storefront including the door jamb. The door jambs are typically pre-fabricated and include a “cut-out” portion to accommodate the dimensions of the doorframe hardware specified by the architect/designer or owner, usually that of the largest selling U.S. manufacturer of such hardware for aluminum/glass doors. The dimensions of the cut-out are therefore commonly either 4⅝ inches in height by 1 9/16 inches in width or 2⅝ inches in height by 1 9/16 inches in width. When the decision is later made by the owner of the retail establishment to install or retrofit a prior art electric strike and associated faceplate into the cut-out portion of the aluminum door jamb, a significant amount of cutting of the door jamb is required, thereby requiring an extended amount of time for the installer and a corresponding high cost.
A still further drawback of prior art electric strike face plates occurs in those installations where the electric strike is required to be installed in door jambs which measure 4 inches or wider and the door is to be center hung. In those instances the auxiliary ramp and face plate comprise two or more pieces, thus again requiring more time for installation than if a one-piece face plate and auxiliary ramp were provided.